Flow through propeller

ABSTRACT

A FLOW THROUGH MARINE PROPELLER UNIT WITH UNIQUE EXHAUST CREEPAGE BARRIER STRUCTURE TO PREVENT CAVITATION AT THE BLADES, SUCH UNIT HAVING THE EXHAUST BARRIER PROTUBERANCE BETWEEN THE REARWARD END OF THE HUB AND THE BLADES TO PREVENT FORWARD CREEPAGE OF EXHAUST GASES, BY CREATING A STAGNANT WATER ZONE AHEAD OF THE FRONT FACE OF THE PROTUBERANCE AND A SHEARING WATER FLOW ACTION AT THE PROTUBERANCE PERIPHERY. THE ANGLE OF THE PROTUBERANCE FRONT FACE TO THE HUB PERIPHERY, AND MORE SPECIFICALLY TO THE AXIS OF THE UNIT, SHOULD BE 90* OR LESS IN A FORWARD DIRECTION WITH RESPECT TO THE DIRECTION OF MOVEMENT OF THE UNIT IN OPERATION.

` FLow THROUGH PRorELL-ER Filed June 24,'1969 1 Y' INVENTORJ I 3. l zoon z. aeg/uz United States Patent O 3,554,665 FLOW THROUGH PROPELLER Eldon L. Lorenz and Robert F. Kress, Grand Rapids, Mich., assignors to Michigan Wheel Company, Grand Rapids, Mich., a corporation of Michigan Filed .lune 24, 1969, Ser. No. 836,093 Int. Cl. B63h l/16, 11/14 U.S. Cl. 416-93 8 Claims ABSTRACT OF THE DISCLOSURE A flow through marine propeller unit with unique exhaust creepage barrier structure to prevent cavitation at the blades, such unit having the exhaust barrier protuberance between the rearward end of the hub and the blades to prevent lforward creepage of exhaust gases, by creating a stagnant water zone ahead of the front face of the protuberance and a shearing water flow action at the protuberance periphery.

The angle of the protuberance front face to the hub periphery, and more specifically to the axis of the unit, should be 90 or less in a forward direction with respect to the direction of movement of the unit in operation.

BACKGROUND OF THE INVENTION This invention relates to marine propeller units that discharge the exhaust gases through a hollow propeller hub.

The problems of cavitation and ventilation around the blade of a marine propeller is present with flow through propellers as with all marine propellers. Hub configuration dictates velocity gradients over the hub and consequently specifies the corresponding pressure gradients. Adverse pressure gradients stimulates cavitation.

Various constructions have been devised in efforts to thwart this undesirable action. One major manufacturer advocates convergent deflection of water around the hub radially inwardly and rearwardly into the exhaust flow, as set lforth in Pat. 3,356,151, in efforts to stop this. Another major manufacturer advocates divergent deflection of water around the hub, radially outwardly and rearwardly away from the exhaust flow as set 'forth in Pat. 2, 948,252, in efforts to stop this.

The effectiveness of both of these opposite techniques has been questioned by some persons in the field. Regardless of this, however, applicants herein have discovered a structural solution to what is believed the fundamental action believed to be causing the cavitation problem of flow through propeller units.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a novel flow through type propeller unit with unique structural features to stop flow of exhaust gases vforward to the blades and prevent adverse pressure gradients. The stuctural solution is simpleand inexpensive, but effective. It creates a gas flow barrier using a stagnant water zone in cooperation with a water shearing action to arrest the forward creepage of exhaust gases. The barrier is created by a special annular protrusion aroundthe hub, between the blades and the rearward end of the hub, the front face of the protrusion being at a controlled angle to cause the barrier.

These and other objects and features of the invention will become apparent upon studying the following description in conjunction with the drawings.

3,554,665 Patented Jan. 12, 1971 BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now specifically to the drawings, the complete assembly 10 includes the typical parts of an outboard marine motor apparatus, including the engine (not shown) from which depends the underwater subassembly 12 to the lower end of the propeller unit or subassembly 14 is attached.

Propeller unit 14 is supported by casing structure 12 of subassernbly 12, with the drive connection including generally vertical, rotational drive shaft 16 powered by the engine and mounted in suitable needle bearings 18 or the like within a central enclosure 20 within outer casing 12. This enclosure 20 extends around shaft 16 within and spaced from outer casing 12 to define an annular exhaust flow passage 22 extending downwardly from the engine to the propeller unit. A bevel type spur gear 24 is fixedly mounted on the lower end of shaft 16, and intermeshes with a bevel type spur gear 26 mounted on and keyed to shaft 28. The forward end of shaft 28, is mounted in a bearing sleeve 30 in a recess in support casing 12. The central portion of shaft 28 is rotationally mounted in bearing 32, and is also supported by bearing assembly 48 around the periphery of the sleeve of spur gear 26 and within an annular support 44 retained between fixed portions 20 and 12 of assembly 12.

The rearward end 28 of shaft 28 is splined, and interfits with a cooperatively configurated rubber bushing 50 that is bonded on its outer periphery to a cylindrical collar 52. This bushing and collar assembly are retained on splined end 28 by a suitable nut 56 threadably engaged to the terminal rear end of shaft 28.

Extending radially outwardly from the periphery of collar or sleeve 52 is a plurality, here three, of struts 60 to the outer ends of which is secured a larger sleeve 62. This hollow outer sleeve extends considerably rearwardly of the rear terminal portion of sleeve 52. It is also radially outwardly spaced from sleeve or collar 52 to define an annular passageway 66 therebetween which merges into a cylindrical passageway 66' beyond the rear end of inner collar 52 and within outer sleeve 62. Annular passageway 66 has the struts 60 at circumferentially spaced intervals therein.

A plurality of propeller 'blades 70 project radially from the outer periphery of sleeve 62. These blades are forwardly of the rearward end of sleeve 62. Sleeves 62 and 52, with their connecting portions, basically comprise the hub of the propeller unit 14.

Preferably, the outer sleeve 6.2 of this hub includes a rearwardly dverging taper on its inner periphery, with rear surface '74 being at a small acute angle to the hub axis, normally about 25. Also, preferably the very terminal edge surface 76 is tapered at a large acute angle to the hub axis, normally around 75. Surface 78 just forwardly of surface 74 may be at a lead-in taper of about 15-20 to the axis if desired.

The outer periphery of sleeve 62 and hence of the hub is generally cylindrical in configuration. Extending around this outer periphery between propeller blades 70 and the rearward end of the hub is a radially outwardly extending annular protrusion ring 90 which performs a special barrier function. This ring may be integral or attached by welding to the hub. It can be located on the hub by an annular shoulder machined into the outer periphery of the hub. It is preferably forwardly of the terminus of the rearward end of the hub. Its forward face is at an angle to cause a stagnated water zone Z immediately forwardly of the protrusion, as shown by the phantom lines in FIG. 3. The angle of this forward face with respect to the hub outer periphery, and specifically with respect to the axis of the propeller unit should normally be no more than about 90, and preferably an acute angle less than 90 e.g, about 70-80". The forward face of this protuberance is also at an acute angle to the outer peripheral surface or edge of the protrusion, which is preferably parallel with the hub axis, forming an annular forward water shearing edge from which the forward face slopes away rearwardly so that this edge is at an acute angle. The water ow over this stagnant zone Z causes a shearing action over the corner slicing edge at the juncture of the front face and peripheral surface as indicated by the arrows in FIG. 3, consequently altering the velocity gradients and therefore the pressure gradient During operation, a small portion of the exhaust gases flowing out the rearward end of the hollow hub tends to curl around the hub edge and follow the low pressure zone that occurs along the hub periphery. This is illustrated by the arrows in FIG. 3. Instead of following the hub up to the blades to cause cavitation or ventilation however, these gases are arrested in zone Z rearwardly of special protrusion 90 and prevented from creeping over this protrusion by the shearing water action in cooperation with the stagnant water zone Z.

It is obvious that various details of construction of the assembly in general may 'be made within the concept while still using the novel exhaust arresting features.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1. A marine propeller unit having a hollow hub with a forward end and a rearward end through which exhaust gases are discharged rearwardly of the hub, and propeller blades extending radially outwardly from said hub, the improvement comprising: the hollow hub having a portion extending rearwardly of the propeller blades, and a water-stagnating annular protrusion projecting radially outwardly from the outer periphery of said rearwardly extending hub portion, said protrusion having a peripheral edge surface, and having a forward face with respect to the direction of travel of said unit at a sufficiently small angle with respect to the axis of said hub to cause a stagnant water barrier adjacent and forwardly of said forward face and a water shearing action over said peripheral edge surface, to arrest forward tiow of exhaust gases tending to cause cavitation at said blades.

2. The propeller unit in claim 1 wherein said forward face is at an angle of no greater than about with respect to the axis of said hub.

3. The propeller unit in claim 2 wherein said angle is an acute angle.

4. The :propeller unit in claim 1 wherein said annular protrusion is spaced forwardly of said hub rearward end.

5. The propeller unit in claim 1 wherein said hub has an inner periphery which tapers outwardly to said rearward end.

6. A marine propeller unit having a hollow hub with a forward end and a rearward end through which exhaust gases are discharged rearwardly of the hub, and propeller blades extending radially outwardly from said hub, the improvement comprising: the hollow hub having a portion extending rearwardly of the propeller blades, an annular protrusion projecting radially outwardly from the outer periphery of said rearwardly extending hub portion said protrusion having an annular forward face and an annular periphery surface cooperatively forming an annular shearing edge at the juncture thereof to cause a gas arresting, water shearing action thereat during operation.

7. The unit in claim 6 wherein forward face slopes rearwardly away `from said shearing edge.

8. The unit in claim 7 wherein said shearing edge has an acute angle.

References Cited UNITED STATES PATENTS 2,213,612 9/1940 Ronning 416-93 2,948,252 8/ 1960 Alexander 416-93 3,246,698 4/ 1966 Kiekhaefer 416-93 3,310,022 3/1967 Kollman 4l6-93UX 3,356,151 12/1967 Strang 416-93 EVERETTE A. POWELL, I R., Primary Examiner 

